Urban-rural integration has been found to be an inevitable trend in the development of urban-rural relations and a vital measure to tackle the unbalanced and uncoordinated development between urban and rural areas. With the continuous promotion of urbanization, the interaction between urban and rural areas is becoming increasingly closer, thus promoting the continuous transformation of urban and rural development. In addition, the connotation of the development of urban-rural integration in accordance with the theory of urban-rural equivalence highlights the “different but equal” nature of urban-rural development. In brief, the integrated development of urban and rural areas should be achieved through the two-way flow of factors and the effective allocation of resources to achieve the interaction and integration of the economic, social and ecological fields of the urban and rural regional systems, and ultimately the development of urban and rural equivalence. The above process also refers to the transformation of the heterogeneous dual structure into a homogeneous monolithic structure, which is essential to the development of urban-rural integration ^[4][6].

    The urban–rural relationship is a vital issue in human social development and has aroused wide attention from scholars worldwide. Urban-rural integration is an advanced stage in the development of urban-rural relations and reflects the evolution of urban-rural relations, which can be traced back to the urban-rural development concept of the ideal socialists ^[4][6]. Existing research on the development of urban-rural integration primarily focuses on the theory of urban-rural relations, connotation elaboration and level measurement, and attempts to measure the level of regional development of urban-rural integration and explore its intrinsic factors by constructing a comprehensive index system ^{[5][6][7][8][9][10][11][12]}[7,8,9,10,11,12,13,14].

    As revealed by the above theoretical analysis, integrated urban-rural development is a complex, multi-level and multi-element composite structural system with profound connotations. The core meaning of urban-rural integrated development lies in the premise of ensuring the effective allocation of urban and rural factors and resources in both directions, realizing the co-prosperity and co-existence of urban and rural areas through the benign interaction between urban and rural areas, realizing the multi-dimensional integrated development of urban and rural areas in economic, social, ecological and spatial aspects, and ultimately realizing the equivalence of urban and rural regional systems ^[7][9]. The specific connotation is presented below. Urban-rural economic integration means that the marginal rewards of urban and rural areas tend to be equal through the two-way flow and optimal allocation of resources and factors under equal economic policies; urban-rural social integration means ensuring that public services (for example., employment, education, medical care and infrastructure) are of equal significance in urban and rural residents; urban-rural ecological integration is achieved through comprehensive and collaborative management of urban and rural regional systems to achieve a state of high integration and complementarity of urban and rural areas. Urban-rural spatial integration refers to the interaction and integration of urban and rural systems in terms of human, logistic and information flows, which is the carrier and basic condition for urban-rural integrated development.

    Under the goal of regional development, integrated urban-rural development should also achieve a unified process of achieving economic-social-ecological benefits of the urban-rural territorial system and a process of spatially balanced development of the urban-rural territorial system ^[13][19]. Accordingly, the theory of regional spatial equilibrium model can be borrowed to construct a spatial equilibrium model of urban-rural integrated development to reveal the inner mechanism of urban-rural integrated development.

Thus, we first assume that under integrated regional urban-rural development, various factors of production (including population) in the region are free to move. The comprehensive development benefits of regional development (ΣFM) consists of social benefit F₁, economic benefit F₂ and ecological benefit F₃; and if it is assumed that a certain type of development benefit AM is composed of land BM, labor CM, technology DM, and capital EM and other factors of production.This model is an extension of the idea of balanced regional development theory and can more effectively explain the inner mechanism of integrated urban-rural development ^[14][22]. Under integrated urban-rural development, through the flow and optimal allocation of factors, urban and rural territorial systems can eventually achieve equal development benefits per capita in urban and rural territorial systems, i.e., eventually realize the equivalence of urban and rural development, and the expression of the model of balanced urban-rural development ^[15][21].In line with the above connotation explanation, the two-way flow of factors between urban and rural areas and the optimal allocation of resources are vital prerequisites for achieving integrated urban-rural development. First, relevant studies have found that China’s urbanization level is still lower than the average of comparable nations in the world ^[16][23]. Second, as the level of integrated development between urban and rural areas is being improved, increasing modernization factors in cities are allocated to rural systems, which are manifested as the net inflow of capital, technology and other factors. Third, with the implementation of the rural revitalization strategy, the proportion of basic public services in rural areas is increasing, which is manifested as an increasing proportion of public goods. Through the flow and optimal allocation of factors between urban and rural areas, the population of rural areas (O₁) tends to decrease within a certain range, along with the continuous promotion of urbanization. Through the input of various factors from cities and the implementation of the rural revitalization strategy, the comprehensive development efficiency of the rural territorial system tends to increase, which means that the per capita development efficiency of the rural territorial system is increasing, and the spatial, economic and social distribution of the urban and rural territorial system is optimized. As a result, the per capita development efficiency of the urban and rural territorial system eventually tends to be equalized, and the integrated development of urban and rural areas is achieved.